Escapement mechanism



1954 c. F. CLIFFORD ESCAPEMENT MECHANISM 2 Sheets-Sheet 1 Filed June 2,1949 Oct, 5, 1954 c. F. CLIFFORD ESCAPEMENT MECHANISM 2 Sheets-Sheet 2Filed June 2, v 1949 Patented Oct. 5, 1954 UNITED STATES 2,690,645PATENT OFFICE Claims priority, application Great Britain June 10, 1948ll Claims.

This invention relates to magnetic escapement mechanism for timepieces,and more particularly to mechanism in which the timekeeping oscillatorconsists of a vibratory magnet attached to a spring and coupled to amagnetic escapement wheel by magnetic forces acting across one or moreair gaps between the escape wheel and the magnet. Such mechanism isdescribed in my prior British patent specification N 0. 596,216.

The present invention concerns primarily, but not exclusively, magneticescapement mechanisms for portable timepieces wherein the vibratorymagnet is carried by the spring to which it is attached and is capableof operating in any position.

The reed and like spring-controlled vibratory armatures capable ofoperating in any position which have hitherto been used for controllingmagnetic escapements -(e. g. as described in my prior specificationabove referred to) have suffered from the disadvantage that they areliable to be disturbed by impact or vibration and thus brought out ofstep with the escape wheel. They are also liable to position error dueto the eliect of gravity upon the oscillatory mass. These undesirableeflects can be minimised by increasing the natural frequency of theoscillatory system, but they cannot be reduced as much as is desired forordinary purposes, except by using an oscillatory system ofinconveniently high natural frequency.

According to the present invention, in order to remove thesedisadvantages, the magnet and the leaf-type spring that carries it arearranged so that the oscillatory axis of the oscillator extendstransversely of the spring intermediate the iongitudinal extent of theoscillator lengthwise of the spring, and preferably through the cent-erof gravity of the oscillator. The oscillatory system is thussubstantially balanced about its oscillatory axis and is therebyrendered substantially insensitive to gravitational forces. The risk ofderangement by inertial forces due to shock is also materially reduced.

While the invention includes arrangements in which the vibratorymovement of the magnet or keeper is substantially a rocking movementabout an axis passing approximately through the centre of gravity of theoscillatory system, it is not restricted to such arrangements, butincludes a modification or development in which a rectilinear vibratorymovement is employed.

The nature of the invention and the manner in which the same is to beperformed will be understood from the following description of severaldifferent examples of escapement mechanisms constructed according to theinvention, reference being made to the accompanying drawings in which:

Figure l is a perspective view showing the essential parts of anescapement mechanism constructed according to a form of the invention 2having a vibratory magnet which extends on op=- posite sides of thesupport to which the spring is attached,

Fig. 1A is a perspective view similar to Fig. .l, the oscillator of theescapement mechanism shown having, however, an oscillatory'axis whichpasses substantially through the center of gravity of the oscillator,

Figures 2, 3 and 4 are similar views of three different examples ofconstruction in which the magnet is located on one side only of thesupport, the required balance being obtained by arranging the spring sothat it extends on both sides of the support,

Figure 5 is a similar view of another modification in which adiiferentm'ode of vibration of the oscillatory system is employed, and

Figure 6 illustrates another modification in which a magnet is arrangedto have a rectilinear vibratory movement due to a third mode ofvibration, i. e. longitudinal.

Corresponding parts are designated by the same reference numerals in thedifferent modifications oi the invention shown in different figures orthe drawings.

The mechanism shown in Figure l of the drawings comprises a vibratorymagnet I carried by a spring 2 that permits its vibration and providesits support, and a magnetic escape wheel 3 on a rotatable spindle 4adapted to be driven by an external driving mechanism such as theclockwork mechanism of a timepiece.

As shown in Figure l, the magnet l is a generally U-s'haped permanentmagnet having inturned ends 5 forming parallel pole faces of oppositemagnetic polarity facing one another across a gap into which the wheel 3projects so that there is a small air gap between each of the pole facesof the magnet l and the adjacent side of the wheel 3.

The spring 2 consists of a fiat leaf-type spring or reed, preferablymade of beryllium, copper or chronovar and is attached to the magnet ithe end thereof remote from the ends 5. It extends in the plane of themagnet I and is attached to a fixed support 6 at a point located, inthis instance, approximately midway between the ends of the magnet I.The spring 2 is thus supported at a point located approximately at thecentre of gravity of the oscillatory system (consisting of the magnet Iand spring 2).

The magnet l is adapted to vibrate under the control of the spring 2 byrocking about an axis parallel to the axis of the spindle 4, so that thepcle-iaces formed by the inturned ends 5 of the magnet vibrate towardsand away from the spindie 4 in planes parallel to the plane of theescape wheel 3.

The vibratory movement of the magnet causes the pole faces of the magnetto move in a wavy oath relatively to the wheel 3 as the wheel rotates.The wheel has a highly permeable magnetic rim l which is shaped tocorrespond as closely as possible with this wavy path having regard tothe varying amplitudes of poles 5. The magnet is thus coupled to thewheel by the magnetic attractive forces acting across the gaps betweenthe inturned ends 5 of the magnet and the rim '1 of the wheel. Themagnetic attraction is suiiiciently powerful to control the rotation ofthe wheel against the torque applied to it through the spindle t so thatthe wheel is constrained to rotate at a speed determined by the naturalfrequency of vibration of the oscillatory system consisting of themagnet I and spring 2.

The oscillatory system is impulsed by the rotation of the wheel 3; and,in order to enable the oscillatory system to vibrate freely at anamplitude determined by the energy of its vibration, the rim I is formedwith magnetic extensions 8 and 9 which form branch extensions of thewavy path and which are arranged so that the polefaces of the magnet canleave the wavy path 1 and move along one of the extensions 8 or 9 ateach extreme of the vibratory movement of the magnet. The extensions 8on one side of the rim I project outwardly, and the extensions 9 on theother side project inwardly and are formed by spokes connecting the rimI to the hub of the wheel.

It will be evident that the axis about which the magnet I vibrates islocated near to the fixed support 6 and on the side thereof remote fromthe inturned ends 5 of the magnet. More particularly, the oscillatoryaxis lies midway of the spring length which connects the magnet I withthe support 6.

The length of the spring 2 is, in this particular instance, so chosenthat the fixed support 6 is located approximately at the centre ofgravity of the oscillatory system. Extremely accurate adjustment of theposition of the support in relation to the centre of gravity is notnecessary, as the system is not overly sensitive to small discrepanciesbetween the position of the support 6 and its theoretically perfectposition to be described presently. Thus, in Fig. 1A the magnet andsupport are so coordinated that the oscillatory axis (do't-and-dashline) of the oscillatory system passes through the center of gravity ofthe latter. The efiect of these arrangements, and especially that ofFig. 1, is that the magnet and spring assembly is substantially balancedabout the oscillatory axis thereof which extends at right-angles to theplane in which the magnet can be moved by flexing the spring 2. Byreason of this substantial or complete balance, the escapement is muchmore resistant to adverse effects of shock and vibration than would bethe case if the oscillatory system were not so balanced. The balancedmounting of the magnet also minimises position error in the timekeepingof the oscillatory system due to the efiect of gravity on saidoscillatory system.

Figure 2 of the drawings shows a modified construction according to theinvention in which the oscillatory system comprises two magnets I in theform of rods or bars attached to the arms of a generally U-shaped spring2 attached to a fixed support 6 by means of a spring tongue 2a which islocated between the outer arms of the U and projects inwards from thebase of the U towards the magnets I. In this construction, the magnets Iare located entirely on one side of the support 6 but the spring 2extends on both sides of the support. The vibratory system consisting ofthe magnets I and spring 2 is substantially balanced in a similar way asthe system described in Figure l, the weight of the magnets I andportion of the spring 2 on one side of the support 6 being in thisinstance approximately balanced by the weight of the portion of thespring 2 on the opposite side of the support 8. The oscillatory axis ofthe instant vibratory system extends transversely of the spring tongue2a somewhere between the ends thereof. Of course, the spring 2 of theinstant vibratory system could, in view of the teaching of Fig. 1A, bereadily arranged so that the oscillatory axis would pass approximatelythrough the center of gravity of the vibratory system.

In the construction shown in Figure 2, the magnets i are not permanentlymagnetised but are made of low-loss magnetic material, e. g. Mumetal andare magnetised by means of a fixed permanent magnet I9 having pole facesII and I2 of opposite magnetic polarity which are located near to but donot touch the outer ends of the magnets. The escape wheel 3 cooperateswith the pole faces on the inner ends of the magnets I in the same wayas the wheel 3 described with reference to Figure 1 cooperates with thepole faces of the magnet shown in that figure.

Figure 3 of the drawings illustrates another modified construction inwhich a permanent bar magnet I is carried by a generally T-shaped spring2 having extensions 3a at the end of the bar of the T, which extensionsare parallel with the stem 3b thereof. The magnet I is fixed to the freeend of the stem 3b, and the spring is supported by attaching the ends ofthe extensions 3a to a pair of fixed supports 6 located on an axis Xwhich passes approximately through the centre of gravity of theoscillatory system consisting of the magnet I and spring 2. Thisconstruction is similar to that shown in Figure 2, in the respect thatthe spring 2 with its stem 31) extends on both sides of the supports 6,so that the magnet l and the portion of the spring 2 to which the magnetis attached is substantially balanced by the portion of the spring 2which extends on the side of the supports 6 remote from the magnet I.Here again, the oscillatory axis of the vibratory system I, 2 extendstransversely of the spring extensions 3a somewhere between the endsthereof. If desired, the spring 2 could be so arranged that theoscillatory axis of the system would pass substantially through thecenter of gravity of the latter.

The magnet I, in the construction shown in Figure 3, cooperates with apair of escape wheels 3 on a common spindle 4 and aligned axially sothat each end of the bar magnet I cooperates with the rim 1 andextensions 8 and 9 on one of the wheels 3. There is, of course, a smallair gap between each end of the magnet i and the adjacent wheel 3.

Figure 4 shows another construction in which a magnet I is carried by agenerally T-shaped spring 2 fixed by extensions 3a to a pair of fixedsupports 6 located on an axis X which passes approximately through thecentre of gravity of the oscillatory system consisting of the magnet Iand spring 2. In this construction, the magnet I is a bar magnet, oneend of which cooperates with an escape wheel 3 on a spindle 4 having itsaxis at right angles to the axis X and to the plane of the spring 2 inthe repose condition of the latter. The escape wheel 3 is of generallycylindrical shape and is formed with a wavy magnetic path I and withextensions 8 and 9 on its circumferential surface of rotation. Themagnet I vibrates, as indicated by the arrows in Figure 4, about an axisextendi-ng transversely of the spring extensions 3a somewhere betweenthe ends thereof, and the surface of the escape wheel 3 is. curved inthe direction of its length to correspond to the curved path of movementof the cooperating pole of the magnet I. There is of course a small airgap between the wheel 3 and the adjacent pole face of the magnet I.

Figure. 5 of the drawings shows another form of construction comprisinga vibratory magnet I attached to the stem 3b of a generally T- shapedspring having extensions 3a by which it is attached to a pair of fixedsupports 6., these supports being located on an axis X which passesapproximately through the centre of gravity of the system consisting ofthe magnet I and spring 2. In this construction, the magnet I is adaptedto vibrate rotationally about the axis of the stem 31) of the spring,the stem 3?) acting as a torsion spring. The magnet I is a generallyU-shaped permanent magnet and has inturned ends 5 adapted to cooperatewith an escape wheel 3 mounted between the poles 5 upon :a spindle 4which has its axis at right-angles to the plane of the spring 2 in itsrepose condition and at right-angles to the axis of rotational vibrationof the magnet I and reed 3b. The escape wheel in this constructionconsists of :a low-loss magnetic disc, e. g. Mumetal, formed with radialcorrugations arranged so that the edge of the disc forms the Wavy path Iwhich cooperates with the pole faces 5 of the armature. The disc isshaped so that the wavy path 1 comprises an odd number of waves, thisbeing necessary to enable the diametrically opposed pole faces of themagnet I to operate in unison.

In the construction shown in Figure 5., the previously describedextensions 8 and 9 of the wavy magnetic path are not used. The vibrationof the magnet must therefore conform approximately in amplitude to theamplitude of the wavy path I. To obtain satisfactory operation underthese conditions, it "is necessary to regulate the torque applied to thespindle 4 so that the amplitude of the oscillation of the magnet due tothe energy transmitted to the oscillatory system conforms very nearly tothe amplitude set by the wavy path I, or the poles of the magnet may bemade thicker (in. the direction of vibration) to give tolerance forvarying amplitudes of vibration.

Figure 6 of the drawings shows another modification of the inventionwhich employs a U- shaped permanent magnet 1 similar to that describedwith reference to Figure l and having inturned ends 5 forming poles ofopposite polarity which face one another across a gap .in which anescape wheel 3 similar to that described with reference to Figure 1 islocated. In the construction shown in Figure 6', the magnet is supportedby means of a control spring 2 in a plane which intersects the axis ofthe escape wheel 3; and it is adapted to vibrate rectilinearly asindicated by the arrows in Figure .6. The spring 2 may be constructed sothat it is more flexible in the direction of its length to make thismode of vibration easier, although a straight spring will vibratelongitudinally at high frequency. The support -6 to which the spring 2is attached is located approximately at the centre of gravity of theoscillatory system consisting of the magnet I and spring 2, so that themagnet is substantially balanced about the support.

As compared with the conventional balance wheel, the vibratory magnetused according to the present invention has the advantage of having nobearings and hence no bearing friction or'wcar.

The balanced arrangement of the magnet enables an oscillatory systemhaving a comparatively low natural frequency (e. g. of the order of from50 cycles per second) to be used without rendering the mechanism undulysensitive to shock and without introducing a serious position error. Aswill be well understood by those skilled in the art, the liability toposition error and the degree of sensitiveness of the mechanism to shockwill depend on the frequency at which the oscillatory system is adaptedto operate. A system of relatively high frequency is inherently moreresistant to shock and less liable to position error. By balancing theassembly in accordance with the present invention, the resistance toshock is considerably increased, and liability to position error isreduced, as compared with. an unbalanced assembly adapted to operate atthe same frequency.

For a portable timepiece such as an alarm clock, it is convenient toadapt the magnet to vibrate at a frequency corresponding to thefrequency of public electricity supply mains (e. g. 50 cycles persecond) as this facilitates stroboscopic adjustment of the oscillatorysystem by merely viewing the magnet assembly in a light fed from themains.

Any convenient method may be employed for adjusting the naturalfrequency of vibration of the oscillatory system for the purpose ofregulating the timepiece. For instance the frequency may be adjusted byloading the magnet I or by altering the effective length of the spring2. Figure l of the drawings shows a simple regulating device whichconsists of an eccentric clamping disc I 2a controlled by means of alever-arm I3. The spring 2 is tightly clamped between a shoulder of thescrew it and the fixed support '6. The disc I2a is spring loaded by aThackery washer I5 against the spring 2. By rotating the eccentric disc32a. by means of the lever I3, the effective length of the spring 2 canbe adjusted for the purpose of regulating the natural frequency of theoscillatory system.

It is to be observed that the spring 2 used in the several constructionsdescribed is inherently rigid in one plane and is arranged so that thisinherent rigidity prevents movement of the magnet or keeper I towards oraway from the escape wheel, and thus maintains the air gap or air gapsbetween the magnet or keeper and escape wheel. It appears further fromthe drawings that the spring 2 is, in its own plane, sufficiently stiffor rigid to be substantially resiliently non-bent in its repose positionin any disposition of the vibratory system.

Unless the magnet is of negligible thickness '(as, for example, in theconstruction shown in Figure 1) it should be halved where it joins thespring so that the latter lies in the thickness of the magnet.Alternatively, the spring could be bent to achieve the same purpose.

I claim:

1. A magnetic escapement mechanism comprising an escape wheel and acooperating oscillator, said oscillator being coupled to said wheel bymagnetic forces and comprising a magnet carried by a leaf-type springand a support to which said spring is attached at a point such that theoscillating movement takes place about an axis extending transversely ofsaid spring and passing substantially through the center of gravity ofthe oscillator.

2. An escapement mechanism according to claim 1 wherein the magnet isadapted to vibrate by bending the spring and the vibratory movementthereof is substantially a rocking movement about a transverse axis ofthe spring passing approximately through the center of gravity of theoscillator.

3. An oscillator, comprising a rigid inertiamember, a leaf-type springcarrying said memher and forming with the latter an oscillatory unit, asupport on which said spring is mounted so that a length of said springconnects said member and support, said member and spring being arrangedso that the latter will, on oscillation of said unit, flex about afixec. transverse axis of said spring which passes substantially throughthe center of gravity of said unit and is spaced from said said supportso that the unit is substantially immune to shock, and means forimpulsing said unit for oscillation of same at its natural frequency.

4. An oscillator, comprising a rigid inertiamember, a leaf-typespring-member carrying said inertia-member, and forming with the latteran oscillatory unit, a support on which said spring-member is mountedintermediate the ends of one of said members so that a length of saidspring member connects said inertia-member and support, said membersbeing arranged so that said spring-member will, on oscillation of saidunit, flex about a fixed transverse axis thereof which passessubstantially through the center of gravity of said unit to provide asubstantially isochronous oscillator which is substantially immune toshock, and means for impulsing said unit for oscillation of same at itsnatural frequency.

5. An oscillator, comprising a rigid inertiamemoer having spacedopposite legs and at least one connecting yoke at adjacent ends of saidlegs, a leaf-type spring extending between said legs and being securedat one end to said yoke, said spring and inertia member together formingan oscillatory unit, a support on which the ther end of said spring ismounted, said member and spring being arranged so that the latter will.on oscillation of said unit, flex about a fixed transverse axis of saidspring which passes substantially through the center of gravity of saidunit, and means for impulsing said unit for oscillation of same at itsnatural frequency.

6. A magnetic escapement mechanism, comprising an escape wheel, amagnet, a leaf-type spring of uniform cross section, said springcarrying said magnet and forming with the latter an oscillatory unitcoupled to said wheel by magnetic forces, and a support on which saidspring is mounted so that a length of said spring connects said magnetand support, the oscillatory axis of said unit extending transversely ofsaid spring between said spring length, and said magnet being arrangedso that the center of gravity of said unit lies substantially in saidoscillatory axis.

7. A substantially isochronous oscillator for use with an escape wheelof a magnetic escapement, comprising a magnet, a leaf-type springcarrying said magnet and forming with the latter an oscillatory unit, asupport on which said spring is mounted so that a length of said springconnects said magnet and support, said magnet and spring being arrangedso that the latter will, on oscillation of said unit, flex about a fixedtransverse axis of said spring which passes substantially through thecenter of gravity of said unit, and magnetic means for impulsing saidunit for oscillation at its natural frequency.

8. A magnetic escapement mechanism, comprising an escape wheel, a magnetmember, a. leaf-type spring member carrying said magnet member andforming with the latter an oscillatory unit coupled to said wheel bymagnetic forces, and a support on which said spring member is mountedintermediate the ends of one of said members so that a length of saidspring member connects said magnet member and support, said membersbeing arranged so that said spring member will, on oscillation of saidunit, flex about a transverse axis thereof which passes substantiallythrough the center of gravity of said unit.

9. A magnetic escapement, comprising an escape wheel, a generallyU-shaped magnet having spaced opposite legs and a connecting yoke, aleaf-type spring extending between said legs and being secured at oneend to said yoke, said spring and magnet together forming an oscillatoryunit coupled to said wheel by magnetic forces, and a support on whichthe other end of said spring is mounted, said magnet and spring beingarranged so that the latter will, on oscillation of said unit, flexabout a transverse axis of said spring which passes substantiallythrough the center of gravity of said unit.

10. An oscillator, comprising a leaf-spring type inertia member adaptedto serve as an oscillatory unit, a support on which said member ismounted intermediate its ends, said member being shaped so that the samewill, on oscillation, flex about a fixed transverse axis thereof passingsubstantially through the center of gravity of said member and spacedfrom said supports so that said unit is substantially isochronous andsubstantially immune to shock, and means for impulsing said unit foroscillation of same at its natural frequency.

11. An oscillator, comprising a rigid inertia member, a leaf-type springof uniform cross section, said spring carrying said member and formingwith the latter an oscillatory unit, a support on which said spring ismounted so that a length of said spring connects said memher andsupport, the oscillatory axis of said unit being fixed and extendingtransversely of said spring midway between said spring length, saidmember being arranged so that the center of gravity of said unit liessubstantially in said oscillatory axis, and means for impulsing saidunit for oscillation of same at its natural frequency.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 554,700 Kohler Feb. 18, 1896 1,522,217 Warren Jan. 6, 19251,771,383 Roe July 22, 1930 1,825,382 Baker Sept. 29, 1931 2,061,047Schweitzer Nov. 17, 1936 2,427,990 Coake Sept. 23, 1947 FOREIGN PATENTSNumber Country Date 277,760 Germany Sept. 4, 1914 451,035 Germany Oct.22, 1927

